Interpretive Summary: E. coli O157:H7 is a pathogen of major concern for the food industry since documentation of its association with several outbreaks of foodborne illness. Undercooked meat and meat products are commonly implicated as transmission vehicles in these outbreaks. This emphasizes the need to better define and quantify the heat treatment given to these foods to provide an adequate degree of protection against survival of E. coli O157:H7. We determined that a heat treatment at 55C for 383 min and at 62.5C for 10.74 min would kill more than one million bacteria per gram of beef. The heating time can be reduced 2-3 fold if beef is supplemented with natural antimicrobials, cinnamaldehyde or carvacrol at 0.5-1 percent cinnamaldehyde or carvacrol. We developed a mathematical model for predicting the destruction of this pathogen in beef. The model can be used to predict the time required at any temperature to kill a certain number of bacteria. This information will be of immediate use to consumers and to the food industry and regulatory agencies to aid in the development of guidelines to ensure safety of the food supply.

Technical Abstract:
The heat resistance of a four-strain mixture of Escherichia coli O157:H7 in raw ground beef in both the absence and presence of the natural antimicrobials, carvacrol and cinnamaldehyde, was tested at temperatures ranging from 55 to 62.5C. Inoculated meat, packaged in bags, was completely immersed in a circulating water bath and cooked for 1 hr to an internal temperature of 55, 58, 60, or 62.5C, and then held for predetermined lengths of time. The surviving bacteria were enumerated by spiral plating onto tryptic soy agar overlaid with Sorbitol MacConkey agar. Inactivation kinetics of the pathogens deviated from first order kinetics. D-values (time in min for the bacteria to decrease by 90%) in the control beef ranged from 63.90 min at 55C to 1.79 min at 62.5C. D-values determined by a logistic model ranged from 43.19 (D1 = D value of a major population of surviving cells) and 89.84 (D2 = D value of a minor subpopulation) at 55 deg C to 1.77 (D1) and 0.78 (D2) at 62.5C. The thermal-death-time (TDT) values suggest that to achieve a 4-D reduction, contaminated processed ground beef should be heated to an internal temperature of 60C for at least 30-32 min. Significant parallel increases (p < 0.05) in sensitivity of the pathogen to heat were observed with the addition and/or increasing levels of carvacrol or cinnamaldehyde from 0.5% to 1.0%. The observed TDT may facilitate the design of acceptance limits of critical control points for ground beef at lower times and temperatures of heating. Mechanistic and dietary aspects and possible benefits of the facilitated inactivation of E. coli in meat for food safety and human health are discussed.